To ensure safe operation of a piston engine, it must be made sure that the piston engine rotates in a predefined direction. A wrong direction of rotation may be triggered in the case of an internal combustion engine, for example, by an erroneous ignition angle output and injection output of a control unit of the engine at start or by a wrong direction of rotation during start as may occur, for example, when the clutch is engaged while the vehicle is rolling backward with a forward gear engaged.
A wrong direction of rotation may result, in the case of an internal combustion engine, for example, in a subsequent start attempt remaining fruitless for some time due to the excessively rich fuel-air mixture. Furthermore, in the event of a wrong direction of rotation there is the risk of damage or destruction of devices in the inlet channel such as, for example, the intake manifold, the throttling device, or a flowmeter. Should the internal combustion engine rotate in the wrong direction, uncontrolled combustion could occur in a cylinder chamber. The inlet valve of the cylinder chamber would be open after the combustion and the hot exhaust gases would enter the inlet channel via the open inlet valve. The devices in the inlet channel could become damaged or destroyed due to a return stroke caused by the uncontrolled combustion in the cylinder and by the high exhaust gas temperatures.
A control unit for detecting the direction of rotation of an internal combustion engine of the above-mentioned type is discussed, for example, in German patent document no. 199 33 845, where the rotation of a camshaft of the internal combustion engine is detected by an absolute phase angle sensor, such as is discussed, for example, in German patent document no. 197 22 016. It is then determined, by querying the absolute phase angle, whether the signal is monotonously increasing or monotonously decreasing. The direction of rotation is determined from this information by a control unit.
In the past, reliable absolute phase angle sensors using the magnetoresistive effect and the Hall effect have been relatively complex components that included at least one control unit and a plurality of sensors.